Safety means for power operated machines



Nov. 21, 1961 l. S. LAWSON ETAL SAFETY MEANS FOR POWER OPERATED MACHINESFiled Sept. 5, 1957 2 Sheets-Sheet 1 III. In [a '6 M/HM K 2. I lnl..MHIHIw m FIG. I

INVENTORJ' IVAR S. LAWSON WALLACE G. RUSSELL imum ATTORNEY Nov. 21, 1961s. LAWSON ETAL SAFETY MEANS FOR POWER OPERATED MACHINES Filed Sept. 5,1957 2 Sheets-Sheet 2 INVENTORS [VAR S. LAWSON WALLACE G. RUSSELL BYATTORNEY tare 3,009,411 SAFETY MEANS FOR POWER OPERATED MACHINES Ivar S.Lawson, RED. 2, Ashvillc, N.Y., and Wallace G. Russell, 315 W. Main St,Falconer, N.Y. Filed Sept. 5, 1957, Ser. No. 682,169 1 Claim. (Cl.10053) This invention relates to power operated machines, such aspresses and the like, and is particularly directed to safety means forsuch machines capable of stopping the operation thereof and thus preventdamage to the machine.

An object of the present invention is to provide a safety guard or meansfor presses or like equipment that stops the operation of the machinewhen an object other than the intended work piece is between the activeparts of the machine. The arrangement is such that any body, foreign tothe work piece, interposed between the moving parts of the machine, willautomatically arrest the movement thereof and necessitate the resettingof the power controls to again initiate the operation of the machine.

This invention contemplates a safety guard means or system for machineshaving means for moving one work part toward another toact on a workpiece disposed between the parts, such machine including manuallycontrolled electrically actuated means for initiating the movement ofthe movable work part into contact with the work piece, and such guardincluding an electronic circuit having a portion adapted to be completedthrough the work parts when a body foreign to the work piece isinterposed between the work parts to impress a small electrical voltageacross the work parts of the machine to de-energize that portion of thecircuit which actuates the machine to instantaneously stop the movementof the movable work part.

Other objects of this invention will appear in the following descriptionand appended claim, reference being had to the accompanying drawingsforming a part of this specification wherein like reference charactersdesignate corresponding parts in the several views.

FIG. 1 is a perspective view of a press provided with or embodying thesafety guard of the invention.

FIG. 2 is a schematic wiring diagram illustrating the circuits embodiedin the invention.

Before explaining in detail the present invention it is to be understoodthat the invention is not limited in its application to the details ofconstruction and arrangement of parts illustrated in the accompanyingdrawings, since the invention is capable of other embodiments and ofbeing practiced or carried out in various ways. Also it is to beunderstood that the phraseolo'gy or terminology employed herein is forthe purpose of description and not of limitation.

In the drawings there is illustrated, by Way of example, a certainembodiment of the present invention as applied to a pneumatic press ofconventional design. The guard consists of a sensitive electronicamplifier controlled by relays in its output circuit in turn connectedto the machine With which the guard is used. The guard is actuated by asmall electrical voltage impressed across the die or tool used in themachine so that during the down stroke of the ram, should the die comein contact with any foreign object, enough current will be conductedthrough it to actuate the amplifier to open or close the relays, as thecase may require, and instantaneously stop movement of the ram. Themachine will remain inoperable until the object causing the stoppage hasbeen removed and a manual reset button on the guard unit returned to thereset position. As a further safety feature, should any external wireleading to the die or to the power source from the guard unit be broken,the machine will be automatically stopped, and will remain inoperativeuntil repairs have been made. For the purpose of operating the guardunit to protect the operator, it is a fact that the human body, or anypart thereof, provides an excellent electrical conductor to energize theguard unit to stop the machine.

Referring to FIG. 1 of the drawings, a machine incorporating the presentinvention has been illustrated. The machine chosen for illustration is apneumatic or air press having relatively movable work parts forperforming an operation on a work piece. The press is inclusive of abase 10 and an upright or standard 12 provided with suitable ways 14. Avertically adjustable head 16 is mounted in the ways 14 and suitablyconnected to an adjusting screw 17 manipulated by hand wheel 18. By suchmeans the head 16 is raised or lowered to desired position with respectto base Ill. Stationary lower die means 20 can be removably secured tobase 10 as by means of studs 21. Movable upper die means 23 mounted on aram 24 cooperate with the lower die to form or otherwise operate on thework piece. Mounted on top of the head 16 is a suitable cylinder 26within which is provided a piston and piston rod connected to ram 24 toreciprocate the latter in'the usual manner. Pressure air is supplied tothe top of cylinder 26 through a pipe 28 coupled to a valve 29. Valve 29is controlled by a solenoid 30 in turn controlled by a foot pedal 32conveniently positioned with respect to the machine. Foot pedal 32 iselectrically connected to solenoid 30 through lead 34, operation of thefoot pedal closing a circuit from the source of energy to be laterdescribed. The operation of valve 29 results in the operation of ram 24to force the same downwardly, causing the upper die 23 to cooperate withthe lower die 20 to operate on the work piece therebetween. When thepressure is removed from the pedal 32, the circuit is opened, valve 29returns to normal position and ram 24 and die 23 return to their raisedor open position. The machine thus far described may be considered asconventional or standard and is intended only to be illustrative of anysuitable mechanism in which are provided relatively movable workengaging members or parts.

As particularly shown in FIG. 2 of the drawings, the safety guardcomprises a main electrical circuit operable to control the energizationof the valve 29 to actuate the ram 24 of the press and a secondaryelectrical circuit operable to instantaneously de-energize the maincircuit and stop the movement of the ram in the event a Short occurs inthe secondary circuit prior to engagement of the upper die with the workpiece. The invention contemplates the use of the secondary circuit tostop press operation in the event that more than one work piece or anunintended object is interposed between the dies as well as theunintentional placing of the operators hand or other part of his bodybetween active parts of the machine.

The electrical portion of the invention has been illustrated as beinginclusive of a high voltage power supply circuit indicated generally insection A, an isolated bias supply indicated generally in section B, adirect coupled amplifier indicated generally in section C, aninterlocked relay circuit indicated generally in section D, and thecooperating movable parts of a machine to be guarded indicated generallyin section E. The secondary or safety circuit is directly connected tothe bias supply the heater element of tube VT1, a filter choke CH4, avariable resistor RE-S in the amplifier circuit and the relay R1.Transformer T-2 has a further secondary 46 to supply the filaments oftubes VT-Z and VT-3 of the direct coupled amplifier. The switch 38 alsocontrols the flow of current from the supply 40 to the primary of biassupply transformers T-1 and T-11, the secondaries 47 and 48 of whichfurnish the grid potential to the input stage VT-2 of the amplifier. Thesecondaries 47 and 48 also furnish current to the safety circuit 50reduced to very low potential by resistors RE-3 and RE-4, to energizerelay R-3.

The main control circuit for the press or machine receives its energyfrom the input supply 40 through the switch 38, lead 37, switch 64, lead34, switch 32 to one side of the load solenoid 30, and from switch 38,lead 36, contacts 57, 58 of relay R2, contacts 60, 61 of relay R1, andcontacts 62, 63 of relay R-3 to the other side of solenoid 30. Switch 32is closed to complete the main control circuit and initiate the movementof the ram 24. Switch 64 is closed during normal operation of the deviceand, upon energization of the guard or auxiliary circuit to stop theoperation of the ram, must be opened to deenergize relays R2 and R1 tocondition the main circuit for normal operation, as hereinafterdescribed.

Relay R-3 is energized from the amplifier circuit after a warm up periodas will be understood. Then upon closing of the manually actuated pressenergizing switch 32 which may be foot or hand operated, current issupplied to the load circuit and the press to energize solenoid 30 toactuate valve 29. Assuming that the proper work piece is between theactive parts of the machine, and that no foreign object such as theoperator's hand is between these parts, the ram 24 will be operated toperform its intended function. However, in the event an improper workpiece or the operators hand is between movable parts of the machine, theram will descend until contact is made with such object, at which timethe safety circuit is energized to cause current to flow from the activeparts of the machine to the ground 22, causing a reversal of current inthe amplifier circuit, energizing relays R-1 and R2, and de-energizingthe solenoid 30 to close valve 29 and stop descent of the ram 24.

To accomplish normal press operations, the instrumentalities associatedwith the ram of the press are shown in section B of the diagram. Here itwill be noted that a double lead 51 is connected to the movable die 23a,each lead in turn being connected to one side of a single pole switch 52and 53 respectively. Switches 52 and 53 are in turn connected bysuitable leads to the safety circuit 50, the switches being providedwith actuating arms 52a, 530, respectively. These switches 52 and 53 areactuated by means such as cam 24a on ram 24, the distance between cam24a and arms 52a, 53a being adjustable in relation to the position ofdie 23a with respect to 20 so that switches 52 and 53 are opened by cam24a pushing downwardly on arms 52a, 53a to disconnect the safety circuitduring the time the die 23!: is in actual contact with the proper workpiece. In other words, the switches are positioned with respect to cam24a so that the guard is effective until the space between the dieswould no longer permit the entrance of any object foreign to the properwork piece. To reset the guard circuit automatically when switches 52and 53 have been opened during normal operation to operate on a workpiece, a switch 55, in series with reset switch 64, is also actuated bymovement of the die member 23a and can be set to be opened during theupstroke of the ram or if desired at the start of the down stroke.Opening of switch 55 which is connected to coil of relay R-2 deenergizesthe relay R-2 and thus R-l, of the interlocked relay circuit.

In order to operate a machine with which the guard has beenincorporated, current for the machine must first pass from contact 57 tocontact 58 of relay R-Z. From contact 58 current is supplied to contacts59 and 60 of relay R-l, which closes the circuit to contact 61. Fromcontact 61 the current passes to contact 62 of relay R-3, which closesthe circuit to contact 63 thereof, completing the circuit to the loadsolenoid of the machine. 'Ihese relays, R-2, R-1, and R-3, control onlythe hot side of the main power line while the return side of the line isconnected through a single point push switch 64, used to reset theguard, and then to the manual switch 32, in turn connected to the otherside of the load solenoid 30. To maintain this condition for normaloperation of the machine with which the guard is used, it is to beunderstood that the coils of relays R-1 and R2 must not be energizedwhile the coil of relay R3 is normally energized.

The coil of relay R-l is connected in series with the plate circuit 66of the direct coupled amplifier in section C of the drawings. Thisamplifier is normally operated in an off condition, the grids of bothtubes being biased strongly negative in relation to the cathodes, thuspreventing the flow of current through the tubes. Both grids of the tubeVT-Z are connected to the positive side of separate isolated DC. powersupplies as shown in section B. The negative sides of both D.C. suppliesare connected through circuits 50 and 51 to an insulated portion of thedies in the controlled machine as above described. It is to be furthernoted that both grids of tube VT-2 are grounded through resistors RE-land RE2 having capacities in the range of 100,000 ohms to 12 megohms, itbeing understood that the greater the resistance of RE1 and RE-2, themore sensitive the guard becomes.

If contact is made between die parts 20 and 23a of the machine by eventhe slightest touch of the operators finger, current will flow throughthe finger from 23a to 20, and to ground 22 and thence from ground tothe grid resistors RE-l and RE-2 and returned to the positive side ofthe bias supply. Such current flow will cause a voltage drop acrossresistors RE1 and REF-2 to produce a positive charge on both grids oftube VT-Z, causing this tube to draw current. Current for tube VI'2 isdrawn through RE-3, and is adjusted so the drop in RE-3 will cause apositive charge to appear on the grid of tube VT-3, bringing it to equalpotential with the cathode, thus causing this tube to draw between 30and 40 milliamperes of plate current, which is more than sufiicient toinsure operation of relay R-1 in series with the plate circuit of VT-3.

When the tube VT-3 draws current, it will energize the coil of relay R1,breaking the contacts between contacts 59, 60, and 61 thereof, instantlyshutting off flow of current to the controlled machine or load. Contacts59 and 60 now being connected to contacts 68 and 69 will cause relay R-2to be energized bridging contacts 57 and 70 and become self holding.Current to the machine or load will be permanently shut off by relay R-2until reset switch 64 is opened to allow relay R-2 to de-energize. It isto be understood that once relay R-1 becomes energized, even if for onlya split second, relay R-2 will be activated and regardless of the factthat should relay R-1 return to normal, no current can be fed to themachine or load because relay R-2 remains self holding until reset.

Relay R3 is normally energized by current from the grid bias supply fromwhich two leads are connected to the die 23a in addition to controllingthe separate grids of tube VT-2, to form a complete circuit for the coilof relay R3. In the event one or both of these wires becomes brokenrelay R-3 will de-energize, breaking contact between contacts 1 and 6thereof, and current to the machine or load will be interrupted. As afurther precaution, the breaking of either of these wires causes thesignal voltage to be fed to the grid circuit of tube VT-2 at the instantof breaking, causing relay R-1 to be momentarily energized. Relay R-2will become self holding and the circuit will be broken not only to therelay R-3 but also to relay R2. The pressing of the reset switch 64under these conditions will not restore current to the machine until thebroken wire has been repaired so that relay R-3 can again be energized.

What is claimed is:

'In a press having a work support and a ram movable toward and away fromthe Work support, die means interposed between the Work support and theram, power means for elfecting movement of said ram toward the worksupport to actuate said die means to perform an operation on a workpiece, a main electrical circuit, control means for said power meansincluding switch means for closing and maintaining said main electricalcircuit energized during normal press operation, means including anormally open secondary electrical circuit com- 1 pleted only by anobject foreign to the normal work piece to de-energize the mainelectrical circuit for stopping the movement of the ram and renderingsaid control means inefiective, and means including manually operablereset switch means to de-energize said secondary circuit so that saidmain electrical circuit can be energized by said control means, saidsecondary circuit including switch means actuated upon predeterminedmovement of the ram to maintain said secondary circuit open duringnormal operation.

References Cited in the file of this patent UNITED STATES PATENTS2,400,486 Carlyle May 21, 1946 2,683,515 Horn et al. July 13, 19542,783,838 Ericson et al. Mar. 5, 1957

